Garret Graves, chairman of Louisiana's Coastal Protection and Restoration Authority, urged a federal judge to "take a hard look" at a plea deal between Halliburton and the Justice Department that would impose the $200,000 fine and three years of probation. Under the deal, Halliburton would plead guilty to a single misdemeanor count of computer fraud involving employees erasing results of computer model tests after the Deepwater Horizon disaster in 2010.

"While it is clear that BP should be the primary focus of this trial, the fine here raises some questions," Graves said in an e-mail message referring to the Halliburton plea agreement.

McCain's criticism came in a letter Thursday asking U.S. Attorney General Eric Holder to justify the proposed fine. The senator also asked Holder to explain whether Halliburton's plea deal would prevent prosecuting company officials, "including managers," for "ordering the destruction of key evidence."

"It is important for the American people to know how effectively the terms of such plea agreements hold accountable those who affirmatively attempted to undermine the investigation into this massive disaster," McCain wrote.

A Justice Department spokesperson assigned to the case wasn't immediately available to answer questions Thursday, the department said. Marc Mukasey, an attorney with the New York firm of Bracewell and Giuliany who is representing Halliburton, declined to comment.

Halliburton is scheduled to formally enter its guilty plea at a Sept. 19 court hearing in New Orleans. U.S. District Judge Jane Triche Milazzo will decide whether to approve the proposed punishment or to reject the plea deal.

McCain, the ranking Republican in the Senate's Permanent Committee on Investigations, said in his letter to Holder that he is concerned about the size of the fine. "I worry that such paltry fines fail to discourage defendants from destroying evidence," the senator wrote. "If the fines do not adequately deter companies, they may begin routinely destroying unfavorable evidence as an acceptable cost of doing business."

The Deepwater Horizon disaster killed 11 people and led to the massive oil spill that "devastated our treasured shores," McCain said.

Also last week, Halliburton announced a pledge to donate $55 million to the National Fish and Wildlife Foundation, which would not be contingent on whether Milazzo accepts the plea deal. Both Graves and McCain also raised questions about the announced donation.

Graves said previous plea agreements with BP and Transocean explicitly committed payments to the NFWF to benefit the Gulf of Mexico's natural resources. Halliburton's plea agreement does not address the $55 million donation.

"With BP and the other responsible parties' continuing to deny their liability here, restoration funds like these play a more important role in the Gulf. Others should not profit for our loss in the Gulf," Graves said in reference to the Halliburton donation.

McCain's letter asked Holder if the Justice Department leaned on Halliburton to make the donation, and if so, why the department thought a donation to the NFWF was the best avenue to help Gulf Coast areas hurt by the spill.

Halliburton was BP's cementing contractor on the Macondo well. But U.S. District Judge Carl Barbier last year ruled that BP's contract protected Halliburton and the energy service firm is exempt from paying most of the pollution claims resulting from the spill. Halliburton last year set aside $300 million as a loss contingency related to the civil trial.